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STRUCTURES IMPLICATED IN THE TRANSPORTATION OF PATHOGENIC FUNGI BY THE EUROPEAN BARK BEETLE, IPS SEXDENTATUS BOERNER: ULTRASTRUCTURE OF A MYCANGIUM

Published online by Cambridge University Press:  31 May 2012

J. Lévieux*
Affiliation:
Station de Zoologie forestière, Ardon, F-45160 Olivet, France
P. Cassier
Affiliation:
Université Paris VI, Cytophysiologie des Arthropodes, 105 Bd Raspail, 75006 Paris, France
D. Guillaumin
Affiliation:
Université Paris VI, Cytophysiologie des Arthropodes, 105 Bd Raspail, 75006 Paris, France
A. Roques
Affiliation:
Station de Zoologie forestière, Ardon, F-45160 Olivet, France
*
1 Author to whom correspondence and reprint requests should be addressed.

Abstract

The European bark beetle, Ips sexdentatus Boerner, carries fungi in puncture pits located on the proximal part of each mandible, the sides of the pronotum, and the elytra.

On the pronotum, each mycangium corresponds to the cup-shaped depression surrounding each seta. Several type III gland cells are associated with each mycangium. The general organization of these cells, commonly found in the epidermis, corresponds to those described by other authors. Their finely granular secretions probably protect the fungi, assure spore adhesion, and also may temporarily inhibit their germination. Similar gland cells were scattered under unspecialized pronotal integument where fungi were not detected.

Thus, it appears that this beetle has evolved a mechanism for the protection or dissemination, or both, of yeasts and fungi such as Ceratocystis sp. This relatively simple system seems to be as efficient as the more evolved mycangia of other species.

Résumé

Le scolyte européen, Ips sexdentatus Boerner, transporte des champignons en plusieurs endroits de sa cuticule. Ces zones sont localisées dans la partie proximale de la mandibule, sur les parties latérales du pronotum et sur les élytres.

Sur le pronotum, chaque mycangium correspond à la dépression en forme de cupule qui entoure chaque soie sensorielle. Ces dépressions communiquent avec plusieurs unités glandulaires de type III appartenant à l’épiderme. Ces cellules sécrétrices s’ouvrent à l’extérieur par de fins canalicules débouchant aux environs de la base de la soie après leur trajet intracuticulaire. L’organisation générale de ces cellules épidermiques peut être aisément comparée à celle décrite par plusieurs auteurs. Leurs sécrétions finement granulaires protègent probablement le champignon avant son inoculation dans le nouvel arbre hôte. Elles pourraient aussi contribuer à l’adhésion des spores sur la cuticule et inhiber temporairement leur germination. Des unités glandulaires identiques existent aussi au niveau des téguments pronotaux où l’on n’a jamais mis en évidence la présence de champignons.

Il apparaît ainsi qu’en utilisant des cellules épidermiques banales, ce scolyte a développé un mécanisme protégeant et facilitant la dissémination de levures et de champignons comme les Ceratocystis. Au point de vue fonctionnel, ce système relativement simple paraît être aussi efficace que les mycangia plus évolués mis en évidence dans d’autres espèces.

[Fourni par les auteurs]

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1991

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